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8.4 Reactions of Alcohols

CH21 –AY 2013-2014 SEM II -- R.D. A. Bolinas. 8.4 Reactions of Alcohols. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes. By protonating –OH in acid , we get an oxonium –OH 2 + that can leave as H 2 O

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8.4 Reactions of Alcohols

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  1. CH21 –AY 2013-2014 SEM II -- R.D. A. Bolinas 8.4 Reactions of Alcohols

  2. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes • By protonating –OH in acid, we get an oxonium –OH2+ that can leave as H2O • E1/E2 depends on the nature of ROH, but usually E1 prevails, except for 1° alcohols (E2)

  3. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes

  4. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes • Predict the major product. Remember Zaitsev’s rule!

  5. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes • Predict the major product. Remember Zaitsev’s rule!

  6. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes • E1cB occurs in biological systems: • the -OH group is two carbons away from a carbonyl (C=O) group

  7. Alcohols can be oxidized into carbonyls…

  8. Alcohols can be oxidized into carbonyls… • We use oxidizing agents: • periodinane(with Iodine in +5 oxidation state) • PRIMARY R-OH TO ALDEHYDE ONLY

  9. Alcohols can be oxidized into carbonyls… • We use oxidizing agents: • Acidic CrO3/CrO42- (with Chromium in +6 oxidation state) • PRIMARY R-OH TO CARBOXYLIC ACID

  10. Alcohols can be oxidized into carbonyls… • Secondary alcohols will give ketones with either reagent

  11. Alcohols can be oxidized into carbonyls…

  12. Alcohols can be oxidized into carbonyls… Periodinane

  13. The Williamson Ether synthesis uses an alkoxide and alkyl halide… • Ethers (R-O-R) • SN2 reaction between R-X and R-O-

  14. The Williamson Ether synthesis uses an alkoxide and alkyl halide… • SN2 reaction between R-X and R-O- • WE NEED TO CONSIDER STERIC HINDERANCE. This might lead to E2! Backside attack is not favorable! Methoxide is also a very strong base.

  15. The Williamson Ether synthesis uses an alkoxide and alkyl halide… • Practice:

  16. The Williamson Ether synthesis uses an alkoxide and alkyl halide… • Practice:

  17. Phenols can sometimes react like alcohols in forming ethers. • CANNOT: be dehydrated with acid, convert into halides with HX • CAN: convert to ether via Williamson ether synthesis, react via EArS (review) The aromatic ring allows the H+ to leave easily, making phenols ACIDIC.

  18. Oxidation of phenols gives us QUINONES • Because they don’t have a hydrogen on the C-OH carbon, phenols become quinones

  19. Oxidation of phenols gives us QUINONES • Quinones easily change form into hydroquinones

  20. Quinones are biologically significant redox facilitators

  21. Ethers generally undergo only acidic cleavages. • Ethers are unreactive to most common reagents • Only strong acids can usually react with them: HI/HBr via SN1 or SN2

  22. Ethers generally undergo only acidic cleavages. • Ethers are unreactive to most common reagents • Only strong acids can usually react with them: HI/HBr via SN1 or SN2 SN1

  23. Cyclic ethers are also generally as unreactive, except for EPOXIDES. • Epoxides come from alkenes + peroxy acids • High angular strain induces reactivity. • SN2 attacks with H3O+ or HX lead to trans-diolor trans-halohydrins, other nucleophiles work too.

  24. Cyclic ethers are also generally as unreactive, except for EPOXIDES. • SN2 attacks with H3O+ or HX lead to trans-diolor trans-halohydrins, other nucleophiles work too. beta-blocker that is used for treatment of cardiac arrhythmias, hypertension, and heart attacks

  25. Sulfur analogs of alcohols and ethers are called thiols and sulfides.

  26. Thiols can be made via SH- and RX, and can react via Williamson mechanism SN2 Synthesis: Williamson thioether synthesis

  27. Disulfides are formed via oxidation. Reduction to thiols can occur as well. http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/r/e/rebonding.jpg http://b.vimeocdn.com/ts/147/230/147230470_640.jpg

  28. Disulfides are formed via oxidation. Reduction to thiols can occur as well. For rebonding: Thioglycolate (acid-like) to convert disulfide bonds in hair protein to thiolates Hydrogen peroxide to oxidize the thiolates back to disulfides. Reforming the disulfides helps re-align amino acids and make hair straight http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/r/e/rebonding.jpg

  29. Disulfides are formed via oxidation. Reduction to thiols can occur as well. “antioxidant” because it protects your cells from oxidative degradation. http://b.vimeocdn.com/ts/147/230/147230470_640.jpg

  30. Propose a synthetic route from 2-phenylethanol to make: E A D B C

  31. Propose a synthetic route from 2-phenylethanol to make: 1. H2SO4 2. H2/Pd H2SO4 KMnO4 Periodinane CrO3

  32. Problems

  33. Problems

  34. More synthetic routes

  35. More synthetic routes

  36. More synthetic routes: propose reagents for each step!

  37. More synthetic routes: propose reagents for each step! Convert to Grignard (Mg/ether) add CH2=O then acid PBr3 NaBH4, H3O+ Periodinane Ph-CH2-MgBr 2. H3O+ conc’dH2SO4

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